Why some of the glass objects recovered from ancient monuments look milky instead of being transparent

Question)

Why some of the glass objects recovered from ancient monuments look milky instead of being transparent?

Answer

When amorphous solids (glass) are heated  and cooled alternately, they acquire crystallinity at the same temperature. Glass objects of ancient time undergo heating due to exposure to sunlight and cooled slowly during night for many years which has resulted in the crystalization of glass object which imparts milky colour to glass of ancient monuments.